JLG 3969electric ANSI Service Manual - Manual (Page 15)

SECTION 2 - PROCEDURES
3120768 – JLG Sizzor –
2-3
NOTE: Start-up of hydraulic system with oil temperatures
below -15° F is not recommended. If it is necessary
to start the system in a sub-zero environment, it will
be necessary to heat the oil with a low density
100VAC heater to a minimum temperature of -15° F.
3. The only exception to the above is to drain and fill
the system with Mobil DTE13 oil or its equivalent.
This will allow start up at temperatures down to -20°
F. However, use of this oil will give poor performance
at temperatures above 120° F. Systems using DTE13
oil should not be operated at temperatures above
200° F under any condition.
Changing Hydraulic Oil
1. Use of any of the recommended hydraulic oils elimi-
nates the need for changing the oil on a regular
basis. However, filter elements must be changed
after the first 40 hours of operation and every 250
hours thereafter. If it is necessary to change the oil,
use only those oils meeting or exceeding the specifi-
cations appearing in this manual. If unable to obtain
the same type of oil supplied with the machine, con-
sult local supplier for assistance in selecting the
proper equivalent. Avoid mixing petroleum and syn-
thetic base oils. JLG Industries recommends chang-
ing the hydraulic oil annually.
2. Use every precaution to keep the hydraulic oil clean.
If the oil must be poured from the original container
into another, be sure to clean all possible contami-
nants from the service container. Always clean the
mesh element of the filter and replace the cartridge
any time the system oil is changed.
3. While the unit is shut down, a good preventive main-
tenance measure is to make a thorough inspection
of all hydraulic components, lines, fittings, etc., as
well as a functional check of each system, before
placing the machine back in service.
Lubrication Specifications
Specified lubricants, as recommended by the component
manufacturers, are always the best choice, however,
multi-purpose greases usually have the qualities which
meet a variety of single purpose requirements. Should
any question arise regarding the use of greases in mainte-
nance stock, consult your local supplier for evaluation.
Refer to Section 1 for an explanation of the lubricant key
designations appearing in the Lubrication Chart.
2.4 CYLINDERS - THEORY OF OPERATION
1. Cylinders are of the double acting type. The Lift and
Steer systems incorporate double acting cylinders.
A double acting cylinder is one that requires oil flow
to operate the cylinder rod in both directions. Direct-
ing oil, by actuating the corresponding control valve
to the piston side of the cylinder, forces the piston to
travel toward the rod end of the barrel, extending the
cylinder rod piston attached to rod. When the oil
flow is stopped, movement of the rod will stop. By
directing oil to the rod side of the cylinder, the piston
will be forced in the opposite direction and the cylin-
der rod will retract.
2. Holding valves are used in the lift circuits to prevent
retraction of the cylinder rod should a hydraulic line
rupture or leak develop between the cylinder and its
related control valve.
2.5 VALVES - THEORY OF OPERATION
Control Valves
It consists of cartridge type valves in an anodized alumi-
num manifold. The cartridge valves provide for control of
flow, volume of flow and pressure in the hydraulic system.
The directional control valves are solenoid operated, three
position, 4-way sliding spool type valves. One valve is pro-
vided for each of the two functions. Energizing one of the
electrical coils on a valve will divert the supply of hydraulic
oil to provide motion of that function in one direction.
Energizing the other coil will divert the oil for motion in the
other direction. When neither coil is energized, the supply
of hydraulic oil is blocked.
Flow control valves in the lift circuits provide for control of
the rate of flow when the oil is flowing out of the cap ends
of the cylinders (the load is being lowered). An adjusting
screw on each cartridge flow control valve allows the rate
of flow (speed) to be adjusted. When oil is flowing into the
cap end of the lift cylinders, an internal check valve feature
allows unrestricted flow.
Pressure relief valves limit the pressure in the steer circuit
and the rod end of each lift cylinder. When the pressure in
one of those circuits reaches the set point of the valve, the
valve opens, allowing enough flow to return to the reser-
voir so that the set pressure is not exceeded. An adjusting
screw on each cartridge relief valve allows the set pres-
sure to be adjusted.
The aluminum manifold provides the passages through
which the hydraulic oil is diverted to provide the desired
movement of the actuators. No moving parts of the valves
slide against the manifold and so it is not subject to wear.